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The Gaia -ESO Survey : Open clusters in Gaia -DR1: A way forward to stellar age calibration

Randich, S.; Tognelli, E.; Jackson, R.; Jeffries, R. D.; Degl'Innocenti, S.; Pancino, E.; Fiorentin, P. Re; Spagna, A.; Sacco, G. and Bragaglia, A., et al. (2018) In Astronomy and Astrophysics 612.
Abstract

Context. Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas. Aims. We describe the methodologies that, taking advantage of Gaia-DR1 and the Gaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators. Methods. We perform a homogeneous analysis of eight open clusters using the Gaia-DR1 TGAS catalogue for bright members and information from the Gaia-ESO Survey for fainter stars. Cluster membership probabilities for the Gaia-ESO Survey targets are derived based on... (More)

Context. Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas. Aims. We describe the methodologies that, taking advantage of Gaia-DR1 and the Gaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators. Methods. We perform a homogeneous analysis of eight open clusters using the Gaia-DR1 TGAS catalogue for bright members and information from the Gaia-ESO Survey for fainter stars. Cluster membership probabilities for the Gaia-ESO Survey targets are derived based on several spectroscopic tracers. The Gaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis. Results. For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017, A&A, 601, A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values. Conclusions. The systematic parallax errors inherent in the Gaia DR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combining Gaia and ground-based spectroscopic datasets.

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@article{4ed7f597-3d9f-42eb-9132-ce67dbb0c0ba,
  abstract     = {<p>Context. Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas. Aims. We describe the methodologies that, taking advantage of Gaia-DR1 and the Gaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators. Methods. We perform a homogeneous analysis of eight open clusters using the Gaia-DR1 TGAS catalogue for bright members and information from the Gaia-ESO Survey for fainter stars. Cluster membership probabilities for the Gaia-ESO Survey targets are derived based on several spectroscopic tracers. The Gaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis. Results. For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017, A&amp;A, 601, A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values. Conclusions. The systematic parallax errors inherent in the Gaia DR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combining Gaia and ground-based spectroscopic datasets.</p>},
  articleno    = {A99},
  author       = {Randich, S. and Tognelli, E. and Jackson, R. and Jeffries, R. D. and Degl'Innocenti, S. and Pancino, E. and Fiorentin, P. Re and Spagna, A. and Sacco, G. and Bragaglia, A. and Magrini, L. and Moroni, P. G.Prada and Alfaro, E. and Franciosini, E. and Morbidelli, L. and Roccatagliata, V. and Bouy, H. and Bravi, L. and Jiménez-Esteban, F. M. and Jordi, C. and Zari, E. and Tautvaišiene, G. and Drazdauskas, A. and Mikolaitis, S. and Gilmore, G. and Feltzing, S. and Vallenari, A. and Bensby, T. and Koposov, S. and Korn, A. and Lanzafame, A. and Smiljanic, R. and Bayo, A. and Carraro, G. and Costado, M. T. and Heiter, U. and Hourihane, A. and Jofré, P. and Lewis, J. and Monaco, L. and Prisinzano, L. and Sbordone, L. and Sousa, S. G. and Worley, C. C. and Zaggia, S.},
  issn         = {0004-6361},
  keyword      = {open clusters and associations: general,Parallaxes,stars: evolution,surveys},
  language     = {eng},
  month        = {04},
  publisher    = {EDP Sciences},
  series       = {Astronomy and Astrophysics},
  title        = {The Gaia -ESO Survey : Open clusters in Gaia -DR1: A way forward to stellar age calibration},
  url          = {http://dx.doi.org/10.1051/0004-6361/201731738},
  volume       = {612},
  year         = {2018},
}